Impact absorbing composites and their production

ABSTRACT

An improved composite for absorbing and dispersing impacting forces is disclosed. The composite includes a flexible plastic enclosure defining an internal cavity. The flexible enclosure is generally impermeable to air and capable of having its internal pressure changed. The composite further includes a foam core filling the cavity and retained within the cavity and adhered on substantially all of its external surface to the internal surface of the cavity. The cavity can be pressurized for higher impact absorbance. Methods for fabricating the composites are disclosed, as well.

This application, filed Sep. 5, 1997, is a continuation of U.S.application Ser. No. 08/253,896, filed Jun. 3, 1994, now abandoned. Ser.No. 08/253,896 is a continuation of Ser. No. 08/027,273, filed Mar. 5,1993 now abandoned, which is a continuation of Ser. No. 07/464,700,filed Jan. 16, 1990, now abandoned; Ser. No. 07/464,700 is acontinuation of Ser. No. 07/370,244, filed Jun. 22, 1989, now abandoned,and of Ser. No. 07/336,563, filed Apr. 10, 1989, now abandoned, which isa continuation of Ser. No. 07/127,145, filed Dec. 1, 1987, nowabandoned; Ser. Nos. 07/370,244 and 07/127,145 are bothcontinuations-in-part of parent Ser. No. 07/099,368, filed Sep. 21,1987, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to improved impact absorbing compressiblecomposites. These composites can be shaped into smooth compound curvesand find application wherever high efficiency impact absorption iscalled for such as in athletic wear, in seating systems, in vehicleinterior padding materials and the like.

2. Background Information

There is a well-recognized need for high performance materials forspreading or absorbing impacts. In recent years, athletes, athleticequipment manufacturers and sports medicine professionals haverecognized the need for improved impact absorbing materials in athleticequipment. These materials find application as heel pads and foot solepads in shoes to absorb the shock of foot strike and as cushioningpoints under football or hockey pads such as shoulder pads, thigh pads,hip pads and the like to name but a few typical applications. Similarneeds may be found in seating systems and in vehicle interiors, to namebut a few representative fields in which impact absorption is a majorinterest.

One common approach to impact absorption in the past has involved usingfelts or blocks of a soft padding material. Padding materials knownheretofore include cotton padding, horsehair padding, foam rubber,foamed plastics, sponge rubber and the like. In these designs, theinherent resilience of the padding material is employed to absorb anddisperse the applied impact. These designs have the disadvantage thatthey often “bottom out” or fully compress on severe impacts of the typeregularly encountered during use such as in athletic equipment or invehicle interiors and thus provide minimal protection. When made thickerto avoid this problem, they become cumbersome and can interfere with thedesign of the article being padded, and in the case of athleticequipment can interfere with the wearer's freedom and performance.

Impact absorbers have also been proposed which employ fluid-filledbladders such as cushioning air sacks These devices rely upon thecompressibility of the enclosed fluid to provide the desired shockabsorbing. In some embodiments of these devices, the fluid is fullyenclosed and can not escape. In others, the fluid is gradually andcontrollably forced out of the bladder during the impact with the rateof release being selected to prevent exhaustion of the fluid during theimpact event. While effective as shock absorbers, these devices can havethe failing of ballooning or otherwise expanding in one region whenanother region is being compressed. This can lead to discomfort or atminimum give an unnatural or unstable feel to the user. In the case offootwear, this problem can lead to an unstable foot plant with increasedopportunity for injury. Another issue with this type of pad has relatedto problems in forming shapes based on compound curve and to retainingstructural integrity with the above-described ballooning.

Representative patents in the field of shock absorbing or impactabsorbing devices include U.S. Pat. No. 4,513,449, SHOCK ABSORBINGATHLETIC EQUIPMENT; U.S. Pat. No. 4,370,754, VARIABLE PRESSURE PAD; U.S.Pat. No. 4,453,271, PROTECTIVE GARMENT; U.S. Pat. No. 4,217,705,SELF-CONTAINED FLUID PRESSURE FOOT SUPPORT DEVICE, all issued to Donzis,U.S. Pat. No. 4,446,634 for FOOTWEAR HAVING IMPROVED SHOCK ABSORPTION;U.S. Pat. No. 4,397,104 for INFLATABLE SOLE-SHOE; U.S. Pat. No.2,863,230 for CUSHIONED SOLE AND HEEL FOR SHOES; U.S. Pat. No. 4,229,889for PRESSURIZED POROUS MATERIAL CUSHION SHOE BASE; U.S. Pat. No.4,637,716 for METHOD FOR MAKING ELASTOMERIC SHOE SOLES; U.S. Pat. No.4,635,384 for FOOTWEAR SOLE; U.S. Pat. No. 4,610,099 for SHOCK-ABSORBINGSHOE CONSTRUCTION; and U.S. Pat. No.4,571,853 for SHOE INSERT.

It is an object of the present invention to provide an improved impactabsorbing composite. It is desired that this composite provide superiorshock absorbing performance and also be capable of being formed intocomplex compound curve shapes, be durable and hygieiic.

STATEMENT OF THE INVENTION

An improved impact absorbing composite has now been found. Thiscomposite is capable of dispersing and absorbing impacting forces withhigh efficiency. The composite is characterized by a structure includinga flexible plastic wall (enclosure) defining an internal cavity. Thisflexible enclosure is made of a material that is generally impermeableto air and is capable of having its internal pressure changed. Theinternal cavity of the enclosure is filled with a foam core. This coreis held in place by the cavity walls. Importantly, the core isintimately adhered (glued, bonded or the like) on substantially all ofits external surfaces to the internal surface of the cavity. Inpreferred embodiments, the wall and the core are prestressed by oneanother. That is, the core presses out against the wall and the wallpushes in against the core. The intimate adherent contact between thefoam core and the outer wall gives rise to an unexpected degree ofproduct integrity and unexpectedly superior impact absorbingcapabilities.

In preferred embodiments, the composite has a valve or fittingcommunicating with the cavity so that the pressure within the cavity canbe altered. This permits the composite to be adjusted to accommodatevarying impacts. The invention can thus include in combination such acomposite together with a device for pressurizing its cavity.

Also in preferred embodiments, the foam core is an open-celled foam or areticulated foam so that the pressure within the core is uniform.Urethane polymers have been found to be excellent for forming the cavityand the foam and are preferred materials of construction.

In other aspects, the composites of the invention can employ coreshaving a plurality of different foams arranged parallel or perpendicularto the impact direction. This permits differing densities and impactresistances to be present at different positions on the composite. Theimpact absorbers of this invention can be used in conjunction with othermaterials or layers including without limitation, cosmetic or hygienicoverlayers, other shock-absorbing layers or the like.

In yet another aspect, this invention provides a variety of methods forfabricating these composites. All of these methods are characterized bycreating an adherent bond between the foam core and the outer layer andby pressurizing the core to a value effective to provide efficientimpact absorption.

One such method involves shaping the wall surface to create a cavity,sizing and shaping the foam core so as to fully fill the cavity andpreferably prestress the wall and core, adhering and enclosing the corewithin the cavity and adjusting the pressure within the cavity to avalue effective to provide efficient impact absorption.

Another fabrication method involves shaping the wall surface to create acavity, sizing and shaping the core so as to partially fill the cavity,placing the core within the cavity forming an elastomeric foam andpreferably an open-celled or reticulated foam in situ within the cavityso as to fill the space between the preshaped foam and the cavity walland to adhere the cavity wall to the core and preferably prestress thewall and core, and adjusting the pressure within the cavity to a valueeffective to provide efficient impact absorption.

Yet another fabrication method involves shaping the wall surface tocreate a cavity, forming a cavity-wall-adherent open-celled orreticulated foam core in situ within the cavity so as to fill the cavityand preferably prestress the wall and core, and adjusting the pressurewithin the cavity to a value effective to provide efficient impactabsorption.

A further fabrication method involves sizing and shaping the foam core,forming the outer wall in situ around and adherent to the foam core suchas by shrinking a film a core-adherent material around the core or byapplying a layer of uncured wall material, such as a solution ofwall-forming polymer, around and adherent to the core and then curingthe uncured wall material, thereby creating a cavity enclosing andpreferably prestressing the core, and adjusting the pressure within thecavity to a value effective to provide efficient impact absorption.

The present shock absorbing composites can be employed in a wide rangeof applications. One excellent application is as heel pads and/or solepads for shoes, especially sport shoes, where they serve to absorb footstrike impact with high efficiency.

The composites of this invention are characterized by being easilyformed in compound curve forms, by being very light weight and by beinghygienic. They are further characterized by being adjustable inpressure, and thus in impact cushioning capacity. This permits them toserve in a wide range of applications with widely variable impacts.

DETAILED DESCRIPTION OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described herein with reference being madeto the accompanying drawings. Where practical in the drawings, a commonreference numeral is used for the same part when it appears in more thanone FIG IN the drawing:

FIG. 1 is an exploded perspective view of the components of an impactabsorber of this invention;

FIG. 2 is an cut away cross-sectional view of a shock absorber of thisinvention;

FIG. 3 is a partially schematic cross sectional view of an impactabsorbing heel pad not embodying this invention. This heel pad has awall defining a pressure-tight cavity but does not have a foam coreadhered to and filling its inner surface. This figure illustrates theflaw in this design that an impact can be absorbed but at the same timeballooning occurs;

FIG. 4 is similar to FIG. 3 but illustrates that with the presentinvention ballooning is prevented;

FIG. 5 is a perspective view of an alternative foam core for use in thisinvention. This core has a plurality of differing compression strengthfoams arranged parallel to the impact force;

FIG. 6 is a cut away cross-sectional view of another alternativeembodiment of the impact absorber of this invention in which the wallmaterial defining the cavity is further shed to provide a supportivecolumn;

FIG. 7 is another cross sectional view of the absorber shown in FIG. 6taken along line 7-7′;

FIG. 8 is an exploded perspective view of the components of the absorberof FIGS. 6 and 7;

FIG. 9 is a perspective view of an alternative embodiment of the impactabsorber of this invention. This embodiment employs a core which has aplurality of differing compression strength foams arranged perpendicularto the impact force;

FIG. 10 is phantom top view of a core configuration for use with closedcell foam materials;

FIG. 11 is a cross sectional view of the core shown in FIG. 10 takenalong line 11-11′;

FIG. 12 is a phantom top view of another core configuration for use withclosed cell foam materials;

FIG. 13 is a cross sectional view of the core shown in FIG. 12 takenalong line 13-13′;

FIG. 14 is a cut away cross sectional view of a shoe containing a shockabsorber of the present invention and additionally having a pump forpressurizing the core of the absorber;

FIG. 15 is a cross sectional view of an automotive dash boardincorporating an impact absorber of this invention;

FIGS. 16 and 17 are two views of an additional representativeapplication or the shock absorbers of this invention as a foot pad;

FIG. 18 is a perspective view of a shoulder pad under pad application orthe shock absorbers of this invention; and

FIGS. 19 and 20 are graphs illustrating the effectiveness of the impactabsorbers of this invention and their adaption to various body weightsand to various impacts.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2 in more detail, these figures illustrate animpact absorber 10. Impact absorber 10 includes a foam core 11 and topand bottom wall sections 12 and 14 which when joined define a cavity 15.A layer of adhesive 16 is present between essentially all of the innersurface of cavity 15 and the outer surface of foam core 11. This layeris shown on core 11 but could as well be on the inside surface of thewall or on both the core and the wall as desired. When wall sections 12and 14 are joined, the cavity which they define is pressure tight. It ispossible to equip the impact absorber with a valve or fitting such asvalve 16. Valve 16 is a “Halkey-Roberts” type urethane valve which isshown in FIG. 1 in its pre-assembly form. After incorporation, the topend of valve 16 is cut off flush with the surface of the shock absorberas shown in FIG. 2. Any equivalent form of valve or pressure controlaperture can be used, if desired. This valve allows the pressure in theinterior (cavity 15) of the impact absorber to be adjusted, as desired,by adding or removing fluid from the cavity.

The outer wall of the impact absorber is formed of flexible plastic. Thematerials used to form the wall can be selected from the film-formingflexible plastics. Virtually any plastic can be used so long as it isresistant to bacterial attack, flexible and shapable into the forms andconfigurations desired. Useful film-forming plastics includepoly(urethane)s both of the poly(ether) and the poly(ester) form,poly(ester)s such as poly(ethylene terphthalate), flexible poly(vinyl)s,elastomeric poly(olefin)s such as poly(isoprene), poly(isobutylene), andneoprene, low density poly(ethylene)s and the like.

In the embodiment shown in FIGS. 1 and 2, the outer wall is preshapedinto the desired configuration and then the foam core is adhered to it.In another embodiment, the outer wall can be formed around the foamcore. One way to accomplish this is to use a liquid polymer precuresolution or suspension which is applied to the outer surface of the coreand then cured. Another way to accomplish this is to use plastic sheetstock and laminate it to the core or shrink it around the core. In anyof these alternative modes of construction, it is essential that therebe a strong adherent bond between the wall and essentially the entireouter surface of the core.

Of the plastics useful in forming the films, preference is given to theflexible poly(urethane)s because of their ready availability. Thesematerials are available from J. P. Stevens Company and DeerfieldUrethane,Inc., to name but two regular suppliers. Representative usefulplastic films include the Deerfield “Dureflex” poly(urethane) films.These materials can be preformed, as in FIGS. 1 and 2 or they can beused as stock goods. When a liquid is used to apply the outer wall, itis typically a solution of a prepolymer or resole resin. Vinyl films canbe used in this application. A typical vinyl film is the vinyl adhesivesealant produced by W. R. Grace and marketed by Eclectic Products asEclectic 6000 adhesive sealant. These materials are solvented inhalocarbons such as perchloroethylene and the like. A preferred liquidcoating is based on the polyurethanes. Again, the nonrigid urethanepolymers are preferred. The solutions known in the art for formingflexible urethane films are very suitable for this application. Typicalurethane polymer solutions include the reaction product of adiisocyanate such as toluene diisocyanate or hexamethylene diisocyanatewith a polyol such as a polyether polyol. These reaction products arecommonly produced in a mixed solvent system such as a polar solvent (forexample, Butyl Cellosolve, Cellosolve Acetate, butyl Carbitol, ordiacetone alcohol or the like) in combination with an aromatic solventsuch as toluene, benzene, or hydrocarbon distillate fractions heavy inaromatics and having a boiling range in the range of from about 140 to240° C. This outer wall, when applied as a liquid can be dried (solventremoved) and cured by the application of heat and/or the application ofa curing catalyst such as an amine. Other curing modalities such asphotocuring can be employed as well, if appropriate. The liquidwall-forming compositions can contain plasticizers and builders and thelike, if desired. The particular conditions used for forming the outerwall are conventional for processing polymers such as the urethaneswhich are preferred and are known to those of skill in the polymer arts.

The outer wall, whether supplied as a preformed structure, a curedliquid overcoat or a shrunk or adhered layer of stock goods is commonlyfrom about 1 to 200 mils in thickness with thicknesses in the range offrom about 2 to 50 mils being preferred and excellent results beingattained with thicknesses of from about 3 to about 35 mils.

The core of the impact absorber is a foam. This foam is preferably anopen-celled foam, that is a foam in which the various cells are incommunication with each other and with the outer surface of the foam.Similar properties are achieved with a reticulated foam, that is a foamwhich has been treated to break down membranes which separated variouscells. Foam rubber, foamed latex, vinyl foams and the like can be used.The preferred foam material for use in the core is poly(urethane) foam.Representative foams include the “Ensolite” foams sold by UniroyalPlastics Co., Inc. and the flexible urethane foams sold by the E. R.Carpenter Company.

Typical densities for the foam core range from between about 0.5 toabout 15 pounds per cubic foot.

Preferred foam densities are from about 2 to 10 pounds per cubic foot.

It will be appreciated that because the foam core is adhered to theouter wall it is in effect a structural member. The adhered foam servesto prevent the ballooning of the device as previously described. Thisduty puts strain upon the foam of the core. If the foam separates underthis strain it can result in a loss of integrity of the device. Withthis potential problem in mind, it is possible to reinforce the foam byincluding filaments or fibers or fabrics in it. Typical reinforcementscan be inorganic materials such as fiberglass or carbon fiber; naturalorganic fibers such as silk, cotton, wool or the like or syntheticorganic fibers such as urethane fibers, nylon filaments, nylon fabrics,aramid filaments and fabrics, and the like. This reinforcement can belaminated into the foam, incorporated into the foam or otherwisecompounded into the foam as is known by those skilled in the art.

In the embodiment shown in FIGS. 1 and 2, the internal foam core ispreshaped to fit tightly within the outer wall of the impact absorber.

This intimate fit may be accomplished in other ways as well. For one,the core can be foamed in place within the wall structure usinginjectable flexible foam forming materials known in the art. With thepreferred urethane foams, a typical foaming mixture can include apolyether polyol, a diisocyanate such as toluene diisocyanate, water,and amine and organotin catalysts. This mixture generally containspolymeric fillers and flexibilizers (plasticizers) as well. The addedwater reacts with the isocyanates to produce an amine plus carbondioxide gas which foams the liquid. Other foaming agents such as gasesincluding carbon dioxide, nitrogen, air or the like as well as lowboiling liquids, (commonly low-boiling fluorocarbons and the like) canalso be added. By controlling the amount of foaming material added andthe cure conditions, the core so formed can, if desired, prestress theouter wall as is preferred. The in situ cores can be closed-cell foams,open-celled foams or reticulated foams as desired.

In a hybrid form of construction, the foam core can be a composite of apreshaped foam body which does not completely fill the cavity created bythe outer wall and an added foam-in-place layer between the wall and thepreshaped body. This form of fabrication has the advantage that thedesired intimate fit is achieved with a minimum of preshaping andfitting while at the same time the preshaped core provides a measure ofdimensional stabilty and integrity to the composite during fabrication.

The third component of the impact absorbers of this invention is anadhesive for affixing the foam core to the wall. This adhesive is mostconveniently an activated adhesive such as a light activated adhesive,UV activated adhesive or heat activated adhesive so as to permit theparts to be fitted together and then bonded. A typical heat-activatedadhesive is the Royal Adhesive DC5 11324 material sold by Uniroyal. Thisadhesive is a two part poly(urethane)/isocyanate adhesive which has theadded advantage of being water-based. When applied to the foam and/orwall it dries to a non-tacky surface which permits easy assembly. Thismaterial heat-activates at 300-325° F. to form a tough adherent bond.Other useful adhesives can include epoxy adhesives, contact cement typepoly(urethane) adhesives such as the Uniroyal “Silaprenes”, the 3M“Scothgrip” adhesives and the isoprene contact cements. In general, onecan employ as adhesive any material which will bond the foam to theouter wall with a strength which will not be exceeded by the forces ofimpact applied to the impact absorber or by the forces applied by thepressure applied to the impact absorber.

In the fabrication methods in which a liquid solution of prepolymer isapplied to the core to create the outer layer or in which the core isfoamed in place, it is often the case that the required intimate bondbetween the core and the outer wall is formed directly without the needfor added adhesive.

The outer wall portions of the impact absorber are joined together suchas by the use of adhesive or by heat sealing or the like to give a fluidimpermeable wall to which the inner core is bonded. After the fusingtogether of the wall components, the impact absorber can be trimmed and,if desired, further shaped to conform to the environment of use.

The core of the present impact absorbers contain a fluid. Gases and inparticular air are very suitable fluids. Liquids and gells could be usedas well, if desired.

Turning to FIGS. 3 and 4, the advantages of the impact absorber of thisinvention are graphically illustrated. In each of these figures a shoe30 is shown together with foot 31 impacting downward into a heel padshown as 32 (in FIG. 3—not according to the invention) and as 10 (inFIG. 4—in accord with this invention). In the case of heel pad 32, thedownward pressure of the heel causes the center of the pad 34 to beseverely depressed while permitting the edges 35 and 36 to balloon up.This can be uncomfortable and unstable. With pad 10 the center 33depresses somewhat but there is minimal ballooning.

Turning now to FIG. 5, a variation of the core 11 is shown. This core(core 50) is fabricated from a plurality of foams of differingproperties, for example density. As shown, the core includes a series ofplugs. 51A, 51B, etc of firm density foam inserted into the body of core11. This can result in a light weight core having the firmness of theplugs. This is merely a representative configuration and one could aswell have one entire section of the core with one density foam andanother section with another density. One could also vary the core basedon other properties, such as the ability of a region of the foam to takea set or the like. The various core sections are adhered to the outerwall of the impact absorber as is shown in FIGS. 1 and 2. One could forma core of this type by placing preshaped pieces of one foam in thecavity and then foaming in place the other material, if desired.

The plastic wall of the impact absorber can have structural propertiesand contribute to the rigidity and shock absorbing properties of thedevice. FIGS. 6, 7 and 8 illustrate an embodiment 60 of the impactabsorber which includes a depression or “column” 61 in its structure soas to provide additional wall surface and structure in that region ofthe absorber. In this embodiment as shown in FIG. 8, the valve 16 isillustrated being laminated into the composite as the top 12 is joinedto the bottom 14.

FIG. 9 illustrates other variations which may be employed withoutdeparting from the spirit of this invention. FIG. 9 shows impactabsorber 80. The foam core of absorber 80 is fabricated from severaldifferent foams including foam section 81, section 82, section 83 andsection 84. These sections are all adhered to the wall 12/14. Valve 16is again provided to permit the pressure of the core to be altered andcontrolled. The various core sections can be adhered to one another, ifdesired. If they are adhered to one another, it must be borne in mindthat the glue layers or the like between the various sections can serveas barriers for the transport of fluid between the various sections. Ifsuch fluid communication is desired, gaps must be left in the gluelayers or glues which are fluid-permeable must be used.

Absorber 80 includes several other features which can be incorporatedinto the present absorbers. An exterior pad 85 is provided. This canprovide additional shock absorbancy. A top layer 86 is also present.This can be a cosmetic over layer or can be provided as a replaceablehygienic layer.

In the absorbers shown in FIGS. 1, 6 and 9, the means for adjusting thepressure (valve 16) has been in communication with the foam core itselfand has relied upon the open-cell foam structure of the core todistribute the applied pressure throughout the core and thus provide auniform level of support throughout the absorber. While this structureis very suitable, one can also employ closed-cell foams, if desired.FIGS. 10 and and FIGS. 12 and 13 respectively illustrate tworepresentative configurations for a closed-cell foam core. In theconfiguration shown in FIGS. 10 and 11, the core 87 contains an aperture88 into which the pressure adjusting valve 16 can fit. This aperture 88communicates with a network of channels 89 spaced throughout the core soas to transmit and distribute the pressure applied to aperture 88. Inthis embodiment, the network of channels is contained by and enclosed bythe closed-cell foam core. This means that the core itself cancontribute to the containment of the pressure applied to the channels.This offers the advantage that localized stress on the outer wall isavoided or minimized and possible failures due to rupture at localizedstress points are minimized.

The configuration shown in FIGS. 12 and 13 is substantially the same asthat shown in FIGS. 10 and 11 with the exception that aperture 97communicates with a network of passages 98 which are not fully containedwithin the core. This configuration does not offer the localized stressrelief of the configuration of FIGS. 10 and 11 but would be lessexpensive and simpler to produce.

Turning to FIG. 14 an additional embodiment of the impact absorber isshown as foot pad 90 housed within the sole portion of shoe 95. Foot pad90 includes the foam core 11 and adherent outer wall 12/14 describedherein. Pad 90 is equipped with a built in pump to alter the pressurewithin its core. This pump includes a one way check valve 16 whichadmits air into pump cavity 91. Pump cavity 91 is compressed andreleased to give a region of low pressure so that air can enter throughvalve 16. When the cavity 91 is depressed again, this forces the newlyadmitted air through passage 92 into the core 11, thus increasing itspressure. This process is repeated until the proper pressure isattained. Shoe 95 also includes a collar 93. This can be formed with thesame structure as pad 90 with an internal core adhered to the walls.Such a collar would be very effective at absorbing the shock which wouldoccur as the wearer's foot comes up in the shoe and impacts it or wouldbe effective as a protection to the wearer's ankle and achilles tendonregion.

FIG. 15 illustrates that the present invention finds application in manyareas beyond athletic equipment. It illustrates an automotive dashboardstructure 101 having an impact pad 100 on its face as well as phantomsteering wheel 102. Impact pad 101 includes core 11, wall 12/14 andvalve 16. Such a pad can provide efficient dashboard impact protectionfor the occupants of the automobile in the event of a crash.

FIGS. 16 and 17 illustrate in two views a ventilated footpad 110 for usein shoes. Pad 110 has a complex shape which requires numerous compoundcurves. In its application as a shoe footpad, pad 110 will be subjectedto a wide variation in impacts depending upon the weight of the runnerusing it and the runner's lightness of footstrike. It is of substantialadvantage to adjust the pressure within the pad with valve 16 toaccommodate these variations.

FIG. 18 illustrates another embodiment of the present invention, anunderpad 180 for use in conjunction with contact sports shoulder pads.Underpad 180 has a structure which includes numerous compound curves anda plurality of “Swiss-cheese” holes through its structure. The compoundcurve-forming ability and the plurality of holes permit the pad toconform to and bend over the wearer's shoulder with comfort andbreathability. It is a special advantage that the present inventionmakes these complex curves possible and provides superior shock andimpact absorption in such settings.

The effectiveness of the present invention can be demonstrated bycomparative tests. A series of impact tests were run on a standardstate-of-the-art basketball shoe. The same tests were then performed onthe same model shoe which had been modified by replacing a portion ofits sole structure (the heel pad region) with an impact absorber of thisinvention. The impact absorber was fabricated from 35 mil flexiblepoly(urethane). The core was about ½ inch thick open-cell poly(urethane)foam of 5 lbs per cubic foot density. The foam core slightly prestressedthe outer wall by being somewhat oversized and was adhered to the wallsusing a heat activated water-based urethane adhesive. Tests were runwith the core sealed at atmospheric pressure and with the corepressurized to 5 and 10 psig. FIGS. 19 and 20 present the results ofthese tests. In each figure line A is the results observed with theprior art shoe. It can be seen that for a given application of energy tothe shoe, i.e. a given impact, the shoe transmits a certain peak forceand a certain acceleration, (in G's) to the wearer. Lines B show theresults achieved when the atmospheric bladder is used. They show thatthe force and acceleration transmitted to the wearer is significantlyreduced. Importantly, this reduction occurs over the entire range ofapplied energies. Thus the effectiveness of the present absorbers issubstantially universal and will be observed with hard impacts such asmay result with heavy athletes and also with lighter impacts such as mayresult with lighter weight athletes, etc.

Lines C show that even better shock absorbancy is achieved when apositive pressure is applied to the bladders. Similar results wereobtained with the 5 and 10 pound pressures which suggest that inpractical terms these pressures may be quite adequate. On the basis ofthese tests, it is believed that pressures in the range of 0 to about 20psig are preferred.

The present invention has been described herein in detail with respectto a number of preferred embodiments and configurations. It will beappreciated, however, that modifications and changes to various aspectsof these embodiments may be made while still coming with in the spiritand scope of this invention which is as defined by the following claims.

What is claimed is:
 1. Apparatus for protecting feet, comprising atennis type shoe suitable for court, field, track and gym sport,comprising a generally flexible upper, a generally flat sole andmechanical means for fastening; the shoe including an inflatable padcompromising a first enclosure formed of material generally impermeableto air and capable of having its internal pressure changed, the padattached to the shoe; a built-in pump attached to the shoe comprising asecond enclosure formed of material generally impermeable to air, thesecond enclosure defining a pump cavity; a passage within the shoeestablishing fluid communication between the first and secondenclosures; and a one-way valve attached to the pump to permit air topass from outside to inside the second enclosure.
 2. The apparatus ofclaim 1 wherein the inflatable pad is located in the sole of the shoe.3. The apparatus of claim 1 wherein the inflatable pad is located in theupper of the shoe.
 4. The apparatus of claim 1 wherein the pump cavityis attached to the upper heel portion of the shoe.
 5. A method forprotecting feet, comprising: attaching an inflatable pad capable ofhaving its internal pressure changed to a tennis type shoe comprising agenerally flexible upper, a generally flat sole and mechanical means forfastening, the shoe being suitable for court, field, track and gymsports; attaching a built-in pump defining a pump cavity to a portion ofthe shoe upper, the pump cavity having a one-way valve; connecting thepump cavity by a passage within the shoe to the inflatable pad; andadjusting the pressure within the pad by repeatedly depressing andreleasing the pump cavity.
 6. The method of claim 5 wherein saidlocation for said inflatable pad comprises said shoe sole.
 7. The methodfor protecting feet of claim 5 wherein said location for said inflatablepad comprises said shoe upper.
 8. Apparatus for protecting feet,comprising: a tennis type shoe suitable for activities that includerunning; inflatable pad means located in said shoe sole for providingcushioning protection against impact and shock attached to said tennistype shoe; and inflation means attached to said shoe upper in fluidcommunication with the pad means for permitting a wearer to alter fluidcontent within the pad while said shoe is worn.
 9. A foot protectionsystem comprising: sport shoe having upper means for enclosing a footwhile engaging in a sport that includes running; lower sole means forcontacting a ground surface while engaging in a sport that includesrunning; an inflatable pad attached to the shoe; and a built-in pumpattached to the shoe, said pump being in fluid communication with saidpad; and wherein the pad is located in a portion of a shoe sole.
 10. Amethod for protecting feet, comprising: attaching an inflatable pad to asport shoe having upper means for enclosing a foot while engaging in asport that includes running, and having lower sole means for contactinga ground surface while engaging in a sport that includes running;attaching a built-in pump to the shoe; and connecting the pump for fluidcommunication with the pad; and that includes attaching the pad to aportion of a shoe sole.